Fuel cells are electrochemical energy conversion devices that convert chemical energy into electrical energy through chemical reactions between hydrogen and oxygen. Typically, hydrogen is either directly supplied to the fuel cell or produced from petrochemicals such as propane, methane, butane, or other source. Fuel cells generally comprise three layered segments: the anode, the membrane or electrolyte, and the cathode. At the anode, a catalyst oxidizes hydrogen gas from a fuel source, converting the hydrogen gas into positively charged ions (hydrogen protons) and negatively charged ions (electrons). The electrolyte or membrane then separates the generated protons and electrons by allowing the protons to pass through while preventing passage of the electrons. The separated electrons travel through a wire, creating the electric current, while the protons travel through the electrolyte to the cathode. While hydrogen is fed to the anode, oxygen (e.g., typically obtained from air) is fed to the cathode where a catalyst creates oxygen ions. Thus, at the cathode, the arriving hydrogen protons and electrons bond with the oxygen ions, creating water and heat as waste products of the reaction. Some of the water is reused or recycled for use in humidification or maintaining the fuel cell's internal temperature and the rest exits through an exhaust pipe.
The electrical energy generated by the above-described components of a fuel cell may be supplied to an external device. Thus, a fuel cell may act as a replacement for conventional sources of electrical energy, such as batteries. Unlike batteries, which store a limited amount of electrical energy chemically (i.e., a thermodynamically closed system), fuel cells consume reactant and oxidant from external sources (i.e., a thermodynamically closed system) and thus can operate continuously such that the reactant and oxidant supplies are maintained.